Abstract
Rat tracheal explants were exposed to N-methyl-N′-nitro-N-nitrosoguanidine (MNNG), a known potent carcinogen, for examination of oncogenic transformation in respiratory tract epithelium in vitro. Organ cultures were exposed for 6 hr on Days 3 and 6 of culture to 0, 0.001, 1.0, or 10.0 µg of MNNG per ml of medium. Primary epithelial cell cultures, derived from 25 of the 30 carcinogen-exposed explants, underwent a distinct morphological change after approximately 160 days of culture. Only after this change could primary cell cultures be subcultured into cell lines. No cell lines could be established from control tissue. Tumorigenicity of the cell lines was determined after approximately 10 or 20 passages by inoculation of 106 cells into the thighs of immunosuppressed isogeneic rats. The number of explants that yielded tumorigenic cell lines was 0, 5, 6, and 9, respectively, for groups of 10 exposed to the above MNNG concentrations. The average latency period between inoculation and tumor appearance also showed a dose response. It was significantly shorter for cell lines in the group receiving 10 µg-MNNG per ml [59.8 ± 7.3 (S.E.) days] than for cell lines in the group receiving 0.001 µg MNNG per ml (125 ± 10.7 days). Either adenosquamous cell carcinomas or keratinizing squamous cell carcinomas were obtained from cell lines in all groups. Four cell lines in the group receiving 10 µg MNNG per ml and 2 cell lines in the group receiving 1 µg MNNG per ml formed tumors which metastasized to other organs.
During culture in vitro, cell lines became increasingly malignant. This was demonstrated by inoculation of some of the cell lines at successive passages. In all cases, tumor incidence increased and the latency period decreased with increasing passage number.
The high frequency of transformation, the dose response, and the production of differentiated epithelial tumors achieved make this culture system a valuable tool for study of the oncogenic transformation of respiratory tract epithelium in vitro.
Footnotes
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↵1 Research jointly sponsored by the National Cancer Institute under Interagency Agreement 40-5-63; the National Institute of Environmental Health Sciences; and the Office of Health and Environmental Research, United States Department of Energy, under Contract W-7405-eng-26 with the Union Carbide Corporation.
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↵2 Supported in part by National Cancer Institute Training Grant CA 05296-01. To whom requests for reprints should be addressed.
- Received March 27, 1979.
- Accepted June 19, 1979.
- ©1979 American Association for Cancer Research.
Volume 39, Issue 10
